Catalysts for Selective Coupling of Olefins, and Methods of Making and Using Same

ABSTRACT

The present invention relates in part to the unexpected discovery of novel complexes capable of catalyzing the selective dehydrogenative coupling of olefins. The invention further relates to the use of these complexes for the selective coupling of olefins.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/579,644, filed Oct. 31, 2017,which application is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under CHE-1205189awarded by National Science Foundation (NSF). The government has certainrights in the invention.

BACKGROUND OF THE INVENTION

1,3-Butadiene is a “platform chemical,” with about 10 M tons per annumproduced for the manufacture of rubbers, polymers and chemicals. Untilrecently, demand for 1,3-butadiene was largely met through itsproduction as a side-product from the cracking of naphtha, drivenprimarily by demand for ethylene. The recent abundance of ethane-richshale gas, however, has shifted the production of ethylene toward thecracking of ethane. This has led to tightening supplies of1,3-butadiene, while demand continues to increase with growth of theglobal economy. As a result, there is renewed interest in thedevelopment of methods for the production of 1,3-butadiene frominexpensive feedstock. The same abundance of ethane that has led todecreased butadiene production from naphtha makes ethylene an attractivepotential feedstock for production of butadiene.

There is thus a need in the art for novel catalysts that can efficientlyand selectively convert ethylene to 1,3-butadiene. In certainembodiments, such novel catalysts can also be used to carry out couplingof additional olefin species to generate conjugated 1,3-dienes. Thepresent invention addresses and meets these needs.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention provides a compound of formula (I), or asalt or solvate thereof:

wherein:

A is selected from the group consisting of H, OH, halide, amine, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, benzyl,

wherein at least one atom or bond in A is optionally coordinated to theIr;

R¹ is selected from the group consisting of H, OH, halide, amine, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl;

each instance of R² is independently selected from the group consistingof H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy,aryl, heteroaryl, and benzyl;

each instance of R³ is independently selected from the group consistingof H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy,aryl, heteroaryl, and benzyl;

each instance of R⁴ is independently selected from the group consistingof H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈heterocycloalkyl, C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl;

X is selected from the group consisting of CH₂, NH, O, and S;

each occurrence of L is independently selected from the group consistingof absent, CO, tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O,benzene, toluene, cyclohexene, cyclooctene, cyclooctadiene,cyclopentene, pyridine, diethyl ether, acetonitrile, triphenylphosphine, N-heterocyclic carbene, C₁₋₆ alcohol, pyrrole, pyrimidine,pyrrolidine, imidazole, and

and

each instance of R^(L) is independently selected from the groupconsisting of H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈alkynyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl,C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl.

In certain embodiments, the compound of formula (I) is a compound offormula (Ia):

In certain embodiments, the compound of formula (I) is a compound offormula:

wherein L is

In certain embodiments, one instance of L is absent and the otherinstance of L is selected from the group consisting of absent, CO,tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O, benzene, toluene,cyclohexene, cyclooctene, cyclooctadiene, cyclopentene, pyridine,diethyl ether, acetonitrile, triphenyl phosphine, N-heterocycliccarbene, C₁₋₆ alcohol, pyrrole, pyrimidine, pyrrolidine, imidazole, and

In other embodiments, L is ethylene.

In another aspect, the invention provides a compound of formula (II), ora salt or solvate thereof:

wherein:

A is selected from the group consisting of H, OH, halide, amine, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, benzyl,

wherein at least one atom or bond in A is optionally coordinated to theIr;

R¹ is selected from the group consisting of H, OH, halide, amine, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl;

each instance of R² is independently selected from the group consistingof H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy,aryl, heteroaryl, and benzyl;

each instance of R³ is independently selected from the group consistingof H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy,aryl, heteroaryl, and benzyl;

each instance of R⁴ is independently selected from the group consistingof H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈heterocycloalkyl, C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl;

X is selected from the group consisting of CH₂, NH, O, and S;

each occurrence of L is independently selected from the group consistingof absent, CO, tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O,benzene, toluene, cyclohexene, cyclooctene, cyclooctadiene,cyclopentene, pyridine, diethyl ether, acetonitrile, triphenylphosphine, N-heterocyclic carbene, C₁₋₆ alcohol, pyrrole, pyrimidine,pyrrolidine, imidazole, and

and

each instance of R^(L) is independently selected from the groupconsisting of H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈alkynyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl,C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl.

In certain embodiments, the compound of formula (II) is:

wherein L is

In yet another aspect, the invention provides a method of catalyticallyconverting an olefin comprising at least one vinylic hydrogen to aconjugated 1,3-diene, the method comprising contacting the olefin with acompound of formula (I), or a salt or solvate thereof.

In certain embodiments, the compound of formula (I) is a compound offormula (IV). In other embodiments, the method comprises firstcontacting a compound of formula (III) with a strong base (B) togenerate a compound of formula (IV), and then contacting the compound offormula (IV) with the olefin, wherein:

wherein either:i) Y is selected from the group consisting of C₁₋₆ carboxylate, C₁₋₆amide, OR^(L), halide, amide, thiolate, oxoanion, C₁₋₆ alkyl, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈ alkynyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl, C₁₋₆perhaloalkyl, aryl, heteroaryl, and benzyl; and L′ is selected from thegroup consisting of absent, CO, tetrahydrofuran, furan, pyran,tetrahydropyran, H₂O, benzene, toluene, cyclohexene, cyclooctene,cyclooctadiene, cyclopentene, pyridine, diethyl ether, acetonitrile,triphenyl phosphine, N-heterocyclic carbenes, C₁₋₆ alcohols, pyrrole,pyrimidine, pyrrolidine, imidazole, and

orii) Y and L′ are a single bidentate ligand selected from the groupconsisting of C₁₋₆ carboxylate and C₁₋₆ amide.

In certain embodiments, the olefin pressure ranges from about 0.1 atm toabout 100 atm. In other embodiments, the catalyst is contacted with thealkene at a temperature of about 100° C. to about 200° C.

In certain embodiments, the olefin comprises ethylene. In otherembodiments, the conjugated 1,3-diene comprises 1,3-butadiene.

In certain embodiments, the catalyst is in solution. In otherembodiments, the solution comprises at least one solvent selected fromthe group consisting of toluene, benzene, xylenes, dioxane, heptane,pyridine, tetrahydrofuran, acetone, acetonitrile, butanol, butanone,carbon tetrachloride, chlorobenzene, chloroform, cyclohexane,dichloroethane, diethylene glycol, diethyl ether, diglyme, dimethylformamide, dimethyl sulfoxide, ethanol, ethyl acetate, ethylene glycol,glycerin, hexamethylphosphoramide, hexamethylphosphorous triamide,hexanes, methanol, methylene chloride, N-methyl-2-pyrrolidinone,nitromethane, pentane, petroleum ether, propanol, and triethylamine. Inyet other embodiments, the solution further comprises at least onehydrogen acceptor additive.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, certain embodiments ofthe invention are depicted in the drawings. However, the invention isnot limited to the precise arrangements and instrumentalities of theembodiments depicted in the drawings.

FIG. 1 is a graph tracking the production of 1,3-butadiene fromethylene, catalyzed by 2. Conditions: 5.0 mM 2 in toluene-4 C₂H₄ (12atm), 110° C., volatiles removed every 5.5 h (upper curve) followed byrecharging with toluene-d₈ and C₂H₄, or allowed to remain in solution(lower curve).

FIGS. 2A-2B are solid-state molecular structures of complex 6. Hydrogenatoms other than those of the iridacyclopentane ring were omitted forclarity in FIG. 2A. Gray unlabeled atoms are carbon atoms, and whiteunlabeled atoms are hydrogen atoms.

FIG. 3 is a free energy profile for ethylene coupling and β-Helimination of the resulting iridacyclopentane determined by DFT.

FIGS. 4A-4D are DFT structures of iridacyclopentane complex 7 (FIG. 4A),agostic iridacyclopentane complex 8 (FIG. 4B), TS for β-H-eliminationTS2 (FIG. 4C), and the initial product of β-H-elimination 9 (FIG. 4D),highlighting the distortion required to allow the agostic interactionand the geometrical similarity of 8, TS2, and 9. H atom undergoingmigration to Ir is marked with an *, other 1,4-butanediyl H atoms areunlabeled. Otherwise, gray unlabeled atoms are carbon atoms, and whiteunlabeled atoms are hydrogen atoms.

FIG. 5 is a free energy profile for butadiene formation following β-Helimination by iridacyclopentane 3.

FIG. 6 is a schematic of a system of the invention describing how themethods of the invention can be coupled to petrochemical crackingprocesses in order to convert raw organic chemical feedstocks into aconjugated 1,3-diene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in part to the unexpected discovery ofnovel complexes capable of catalyzing selective dehydrogenative couplingof olefins. The invention further relates to the use of these complexesfor selective dehydrogenative coupling of olefins.

Definitions

As used herein, each of the following terms has the meaning associatedwith it in this section.

Unless defined otherwise, all technical and scientific terms used hereingenerally have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs. Generally,the nomenclature used herein and the laboratory procedures in separationscience, organometallic chemistry, inorganic chemistry, and organicchemistry are those well-known and commonly employed in the art.

As used herein, the articles “a” and “an” refer to one or to more thanone (i.e., to at least one) of the grammatical object of the article. Byway of example, “an element” means one element or more than one element.

As used herein, the term “about” is understood by persons of ordinaryskill in the art and varies to some extent on the context in which it isused. As used herein when referring to a measurable value such as anamount, a temporal duration, and the like, the term “about” is meant toencompass variations of ±20% or ±10%, more preferably ±5%, even morepreferably ±1%, and still more preferably ±0.1% from the specifiedvalue, as such variations are appropriate to perform the disclosedmethods.

As used herein, the term “alkenyl,” employed alone or in combinationwith other terms, means, unless otherwise stated, a stablemonounsaturated or di-unsaturated straight chain or branched chainhydrocarbon group having the stated number of carbon atoms. Examplesinclude vinyl, propenyl (or allyl), crotyl, isopentenyl, butadienyl,1,3-pentadienyl, 1,4-pentadienyl, and the higher homologs and isomers. Afunctional group representing an alkene is exemplified by —CH₂—CH═CH₂.

As used herein, the term “alkoxy” employed alone or in combination withother terms means, unless otherwise stated, an alkyl group having thedesignated number of carbon atoms, as defined above, connected to therest of the molecule via an oxygen atom, such as, for example, methoxy,ethoxy, 1-propoxy, 2-propoxy (isopropoxy) and the higher homologs andisomers. A specific example is (C₁-C₃)alkoxy, such as, but not limitedto, ethoxy and methoxy.

As used herein, the term “alkyl,” by itself or as part of anothersubstituent means, unless otherwise stated, a straight or branched chainhydrocarbon having the number of carbon atoms designated (i.e., C₁-C₁₀means one to ten carbon atoms) and includes straight, branched chain, orcyclic substituent groups. Examples include methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, andcyclopropylmethyl. A selected example is (C₁-C₆)alkyl, such as, but notlimited to, ethyl, methyl, isopropyl, isobutyl, n-pentyl, n-hexyl andcyclopropylmethyl.

As used herein, the term “alkynyl,” employed alone or in combinationwith other terms, means, unless otherwise stated, a stable straightchain or branched chain hydrocarbon group with a triple carbon-carbonbond, having the stated number of carbon atoms. Non-limiting examplesinclude ethynyl and propynyl, and the higher homologs and isomers. Theterm “propargylic” refers to a group exemplified by —CH₂—C≡CH. The term“homopropargylic” refers to a group exemplified by —CH₂CH₂—C≡CH. Theterm “substituted propargylic” refers to a group exemplified by—CR₂—C≡CR′, wherein each occurrence of R′ is independently H, alkyl,substituted alkyl, alkenyl or substituted alkenyl, with the proviso thatat least one R′ group is not hydrogen. The term “substitutedhomopropargylic” refers to a group exemplified by —CR′₂CR′₂—C≡CR′,wherein each occurrence of R′ is independently H, alkyl, substitutedalkyl, alkenyl or substituted alkenyl, with the proviso that at leastone R′ group is not hydrogen.

As used herein, the term “aromatic” refers to a carbocycle orheterocycle with one or more polyunsaturated rings and having aromaticcharacter, i.e. having (4n+2) delocalized π (pi) electrons, where n isan integer.

As used herein, the term “aryl,” employed alone or in combination withother terms, means, unless otherwise stated, a carbocyclic aromaticsystem containing one or more rings (typically one, two or three rings)wherein such rings may be attached together in a pendent manner, such asa biphenyl, or may be fused, such as naphthalene. Examples includephenyl, anthracyl, and naphthyl.

As used herein, the term “aryl-(C₁-C₃)alkyl” refers to a functionalgroup wherein a one to three carbon alkylene chain is attached to anaryl group, e.g., —CH₂CH₂-phenyl or —CH₂-phenyl (benzyl). Specificexamples are aryl-CH₂— and aryl-CH(CH₃)—. The term “substitutedaryl-(C₁-C₃)alkyl” refers to an aryl-(C₁-C₃)alkyl functional group inwhich the aryl group is substituted. A specific example is substitutedaryl(CH₂)—. Similarly, the term “heteroaryl-(C₁-C₃)alkyl” refers to afunctional group wherein a one to three carbon alkylene chain isattached to a heteroaryl group, e.g., —CH₂CH₂-pyridyl. A specificexample is heteroaryl-(CH₂)—. The term “substitutedheteroaryl-(C₁-C₃)alkyl” refers to a heteroaryl-(C₁-C₃)alkyl functionalgroup in which the heteroaryl group is substituted. A specific exampleis substituted heteroaryl-(CH₂)—.

As used herein, the term “conjugated 1,3-diene” refers to a moleculethat comprises the group

wherein R′ and R″ are independently H or a non-H-substituent. In certainembodiments, the conjugated 1,3-diene is 1,3-butadiene.

As used herein, the term “cracking” refers to the petrochemistry processwhereby complex organic molecules are broken down into lower-molecularweight molecules through the breaking of carbon-carbon bonds and/or lossof hydrogen gas.

As used herein, the term “cycloalkyl,” by itself or as part of anothersubstituent refers to, unless otherwise stated, a cyclic chainhydrocarbon having the number of carbon atoms designated (i.e., C₃-C₆refers to a cyclic group comprising a ring group consisting of three tosix carbon atoms) and includes straight, branched chain or cyclicsubstituent groups. Examples include cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Other examples are(C₃-C₆)cycloalkyl, such as, but not limited to, cyclopropyl, cyclobutyl,cyclopentyl and cyclohexyl.

As used herein,

refers to a side-on bound ethylene. The dashed bond to the center of theethylene denotes an η² coordination to a metal center. Analogously,

refers to a side-on bound ethylene substituted with R^(L). Thesubstitutions on the ethylene are as defined elsewhere herein,constituting a genus of η² coordinated olefin ligands.

As used herein, the term “halide” refers to a halogen atom bearing anegative charge. The halide anions are fluoride (F⁻), chloride (Cl⁻),bromide (Br⁻), and iodide (I⁻).

As used herein, the term “halo” or “halogen” alone or as part of anothersubstituent refers to, unless otherwise stated, a fluorine, chlorine,bromine, or iodine atom.

As used herein, the term “heteroalkenyl” by itself or in combinationwith another term refers to, unless otherwise stated, a stable straightor branched chain monounsaturated or diunsaturated hydrocarbon groupconsisting of the stated number of carbon atoms and one or twoheteroatoms selected from the group consisting of O, N, and S, andwherein the nitrogen and sulfur atoms may optionally be oxidized and thenitrogen heteroatom may optionally be quaternized. Up to two heteroatomsmay be placed consecutively. Examples include —CH═CH—O—CH₃,—CH═CH—CH₂—OH, —CH₂—CH═N—OCH₃, —CH═CH—N(CH₃)—CH₃, and —CH₂—CH═CH—CH₂—SH.

As used herein, the term “heteroalkyl” by itself or in combination withanother term refers to, unless otherwise stated, a stable straight orbranched chain alkyl group consisting of the stated number of carbonatoms and one or two heteroatoms selected from the group consisting ofO, N, and S, and wherein the nitrogen and sulfur atoms may be optionallyoxidized and the nitrogen heteroatom may be optionally quaternized. Theheteroatom(s) may be placed at any position of the heteroalkyl group,including between the rest of the heteroalkyl group and the fragment towhich it is attached, as well as attached to the most distal carbon atomin the heteroalkyl group. Examples include: —O—CH₂—CH₂—CH₃,—CH₂—CH₂—CH₂—OH, —CH₂—CH₂—NH—CH₃, —CH₂—S—CH₂—CH₃, and —CH₂CH₂—S(═O)—CH₃.Up to two heteroatoms may be consecutive, such as, for example,—CH₂—NH—OCH₃, or —CH₂—CH₂—S—S—CH₃.

As used herein, the term “heterocycle” or “heterocyclyl” or“heterocyclic” by itself or as part of another substituent refers to,unless otherwise stated, an unsubstituted or substituted, stable, mono-or multi-cyclic heterocyclic ring system that consists of carbon atomsand at least one heteroatom selected from the group consisting of N, O,and S, and wherein the nitrogen and sulfur heteroatoms may be optionallyoxidized, and the nitrogen atom may be optionally quaternized. Theheterocyclic system may be attached, unless otherwise stated, at anyheteroatom or carbon atom that affords a stable structure. A heterocyclemay be aromatic or non-aromatic in nature. In certain embodiments, theheterocycle is a heteroaryl.

As used herein, the term “heteroaryl” or “heteroaromatic” refers to aheterocycle having aromatic character. A polycyclic heteroaryl mayinclude one or more rings that are partially saturated. Examples includetetrahydroquinoline and 2,3-dihydrobenzofuryl.

Examples of non-aromatic heterocycles include monocyclic groups such asaziridine, oxirane, thiirane, azetidine, oxetane, thietane, pyrrolidine,pyrroline, imidazoline, pyrazolidine, dioxolane, sulfolane,2,3-dihydrofuran, 2,5-dihydrofuran, tetrahydrofuran, thiophane,piperidine, 1,2,3,6-tetrahydropyridine, 1,4-dihydropyridine, piperazine,morpholine, thiomorpholine, pyran, 2,3-dihydropyran, tetrahydropyran,1,4-dioxane, 1,3-dioxane, homopiperazine, homopiperidine, 1,3-dioxepane,4,7-dihydro-1,3-dioxepin and hexamethyleneoxide.

Examples of heteroaryl groups include pyridyl, pyrazinyl, pyrimidinyl(such as, but not limited to, 2- and 4-pyrimidinyl), pyridazinyl,thienyl, furyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, pyrazolyl,isothiazolyl, 1,2,3-triazolyl, 1,2,4-triazolyl, 1,3,4-triazolyl,tetrazolyl, 1,2,3-thiadiazolyl, 1,2,3-oxadiazolyl, 1,3,4-thiadiazolyland 1,3,4-oxadiazolyl.

Examples of polycyclic heterocycles include indolyl (such as, but notlimited to, 3-, 4-, 5-, 6- and 7-indolyl), indolinyl, quinolyl,tetrahydroquinolyl, isoquinolyl (such as, but not limited to, 1- and5-isoquinolyl), 1,2,3,4-tetrahydroisoquinolyl, cinnolinyl, quinoxalinyl(such as, but not limited to, 2- and 5-quinoxalinyl), quinazolinyl,phthalazinyl, 1,8-naphthyridinyl, 1,4-benzodioxanyl, coumarin,dihydrocoumarin, 1,5-naphthyridinyl, benzofuryl (such as, but notlimited to, 3-, 4-, 5-, 6- and 7-benzofuryl), 2,3-dihydrobenzofuryl,1,2-benzisoxazolyl, benzothienyl (such as, but not limited to, 3-, 4-,5-, 6-, and 7-benzothienyl), benzoxazolyl, benzothiazolyl (such as, butnot limited to, 2-benzothiazolyl and 5-benzothiazolyl), purinyl,benzimidazolyl, benztriazolyl, thioxanthinyl, carbazolyl, carbolinyl,acridinyl, pyrrolizidinyl, and quinolizidinyl.

The aforementioned listing of heterocyclic and heteroaryl moieties isintended to be representative and not limiting.

As used herein, the term “ligand” refers to any organic or inorganicmolecule or ion that is capable of coordinating to a metal center. Incertain embodiments, the ligand comprises one or more lone electrons orelectron pairs that can coordinate with a metal center.

As used herein, the term “substituted” refers to that an atom or groupof atoms has replaced hydrogen as the substituent attached to anothergroup.

As used herein, the term “substituted alkyl,” “substituted cycloalkyl,”“substituted alkenyl” or “substituted alkynyl” refers to alkyl,cycloalkyl, alkenyl or alkynyl, as defined above, substituted by one,two or three substituents selected from the group consisting of halogen,—OH, alkoxy, tetrahydro-2-H-pyranyl, —NH₂, —N(CH₃)₂,(1-methyl-imidazol-2-yl), pyridin-2-yl, pyridin-3-yl, pyridin-4-yl,—C(═O)OH, trifluoromethyl, —C(═O)O(C₁-C₄)alkyl, —C(═O)NH₂,—C(═O)NH(C₁-C₄)alkyl, —C(═O)N((C₁-C₄)alkyl)₂, —SO₂NH₂, —C(═NH)NH₂, and—NO₂, preferably containing one or two substituents selected fromhalogen, —OH, alkoxy, —NH₂, trifluoromethyl, —N(CH₃)₂, and —C(═O)OH,more preferably selected from halogen, alkoxy and —OH. Examples ofsubstituted alkyls include, but are not limited to, 2,2-difluoropropyl,2-carboxycyclopentyl and 3-chloropropyl.

For aryl, aryl-(C₁-C₃)alkyl and heterocyclyl groups, the term“substituted” as applied to the rings of these groups refers to anylevel of substitution, namely mono-, di-, tri-, tetra-, orpenta-substitution, where such substitution is permitted. Thesubstituents are independently selected, and substitution may be at anychemically accessible position. In certain embodiments, the substituentsvary in number between one and four. In another embodiment, thesubstituents vary in number between one and three. In yet anotherembodiment, the substituents vary in number between one and two. In yetanother embodiment, the substituents are independently selected from thegroup consisting of C₁₋₆ alkyl, —OH, C₁₋₆ alkoxy, halo, amino, acetamidoand nitro. As used herein, where a substituent is an alkyl or alkoxygroup, the carbon chain may be branched, straight or cyclic.

In certain embodiments, an optional substituent is selected from thegroup consisting of C₁-C₆ alkyl, C₃-C₈ cycloalkyl, phenyl, C₁-C₆hydroxyalkyl, (C₁-C₆ alkoxy)-C₁-C₆ alkyl, C₁-C₆ haloalkyl, C₁-C₆haloalkoxy, halogen, —CN, —OR^(b), —N(R^(b))(R^(b)), —NO₂,—C(═O)N(R^(b))(R^(b)), —S(═O)₂N(R^(b))(R^(b)), acyl, and C₁-C₆alkoxycarbonyl, wherein each occurrence of R^(b) is independently H,C₁-C₆ alkyl, or C₃-C₈ cycloalkyl, wherein in R^(b) the alkyl orcycloalkyl is optionally substituted with at least one selected from thegroup consisting of halogen, —OH, C₁-C₆ alkoxy, and heteroaryl; orsubstituents on two adjacent carbon atoms combine to form —O(CH₂)₁₋₃O—.

In certain embodiments, an optional substituent is selected from thegroup consisting of C₁-C₆ alkyl, C₃-C₈ cycloalkyl, phenyl, C₁-C₆hydroxyalkyl, (C₁-C₆ alkoxy)-C₁-C₆ alkyl, C₁-C₆ haloalkyl, C₁-C₆haloalkoxy, halogen, —OR^(b), and —C(═O)N(R^(b))(R^(b)), wherein eachoccurrence of R^(b) is independently H, C₁-C₆ alkyl, or C₃-C₈cycloalkyl, wherein in R^(b) the alkyl or cycloalkyl is optionallysubstituted with at least one selected from the group consisting ofhalogen, —OH, C₁-C₆ alkoxy, and heteroaryl; or substituents on twoadjacent carbon atoms combine to form —O(CH₂)₁₋₃O—.

In certain embodiments, an optional substituent is selected from thegroup consisting of C₁-C₆ alkyl, —OH, C₁-C₃ haloalkyl, C₁-C₆ alkoxy,C₃-C₈ cycloalkyl, C₃-C₈ cycloalkoxy, halo, and —CN.

Ranges: throughout this disclosure, various aspects of the invention canbe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible sub-ranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual and partialnumbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6.This applies regardless of the breadth of the range.

Disclosure

The present invention relates to the unexpected discovery of noveltransition metal catalysts that are useful in the dehydrogenativecoupling of olefins. In certain embodiments, the catalysts are capableof carrying out the selective and efficient conversion of ethylene to1,3-butadiene.

In one aspect, the invention provides a compound of formula (I), or asalt or solvate thereof:

wherein;

A is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, optionally substituted benzyl,

wherein at least one atom or bond in A is optionally coordinated to theIr;

R¹ is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, and optionally substitutedbenzyl;

each instance of R² is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R³ is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈ heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R⁴ is independently selected from the group consistingof H, optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl;

X is selected from the group consisting of CH₂, NH, O, and S;

each occurrence of L is independently selected from the group consistingof absent, CO, tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O,benzene, toluene, cyclohexene, cyclooctene, cyclooctadiene,cyclopentene, pyridine, diethyl ether, acetonitrile, triphenylphosphine, N-heterocyclic carbene, C₁₋₆ alcohol, pyrrole, pyrimidine,pyrrolidine, imidazole, and

and

each instance of R^(L) is independently selected from the groupconsisting of H, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₂-C₈ alkenyl,optionally substituted C₂-C₈ alkynyl, optionally substituted C₁-C₈heteroalkyl, optionally substituted C₃-C₈ heterocycloalkyl, optionallysubstituted C₂-C₈ heteroalkenyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl.

In certain embodiments, the compound of formula (I) is a compound offormula (Ia):

wherein R¹, R², R³, R^(L), X and L are as defined in formula (I).

In certain embodiments, the compound of formula (I) is:

wherein L is

(ethylene).

In certain embodiments, one instance of L is absent while the otherinstance of L is not.

In certain embodiments, the compound of formula (I) comprises an Ir (I).

In another aspect, the invention provides a compound of formula (II), ora salt or solvate thereof:

wherein;

A is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, optionally substituted benzyl,

wherein at least one atom or bond in A is optionally coordinated to theIr;

R¹ is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, and optionally substitutedbenzyl;

each instance of R² is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈ heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R³ is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈ heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R⁴ is independently selected from the group consistingof H, optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl;

X is selected from the group consisting of CH₂, NH, O and S;

each occurrence of L is independently selected from the group consistingof absent, CO, tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O,benzene, toluene, cyclohexene, cyclooctene, cyclooctadiene,cyclopentene, pyridine, diethyl ether, acetonitrile, triphenylphosphine, N-heterocyclic carbene, C₁₋₆ alcohol, pyrrole, pyrimidine,pyrrolidine, imidazole, and

and

each instance of R^(L) is independently selected from the groupconsisting of H, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₂-C₈ alkenyl,optionally substituted C₂-C₈ alkynyl, optionally substituted C₁-C₈heteroalkyl, optionally substituted C₃-C₈ heterocycloalkyl, optionallysubstituted C₂-C₈ heteroalkenyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl.

In certain embodiments, the compound of formula (II) is:

wherein L is

(ethylene).

In certain embodiments, the compound of formula (II) comprises an Ir(I).

In another aspect, the invention provides compounds, which areprecatalysts and, upon activation, can be used for the catalytichomocoupling of olefins. In certain embodiments, a precatalyst of theinvention is a compound of formula (III), or a salt or solvate thereof:

wherein;

A is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, optionally substituted benzyl,

wherein at least one atom or bond in A is optionally coordinated to theIr;

R¹ is selected from the group consisting of H, OH, halide, amine,optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionally substitutedaryl, optionally substituted heteroaryl, and optionally substitutedbenzyl;

each instance of R² is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈ heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R³ is independently selected from the group consistingof H, OH, halide, amine, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₁-C₈ heteroalkyl,optionally substituted C₃-C₈ heterocycloalkyl, optionally substitutedC₁₋₆ perhaloalkyl, optionally substituted C₁₋₆ alkoxy, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl;

each instance of R⁴ is independently selected from the group consistingof H, optionally substituted C₁₋₆ alkyl, optionally substituted C₃-C₈cycloalkyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl;

X is selected from the group consisting of CH₂, NH, O, and S;

Z is selected from the group consisting of H, C₁₋₆ carboxylate, OR^(L),halide, amide, thiolate, oxoanion, C₁₋₆ alkyl, optionally substitutedC₁₋₆ alkyl, optionally substituted C₃-C₈ cycloalkyl, optionallysubstituted C₂-C₈ alkenyl, optionally substituted C₂-C₈ alkynyl,optionally substituted C₁-C₈ heteroalkyl, optionally substituted C₃-C₈heterocycloalkyl, optionally substituted C₂-C₈ heteroalkenyl, optionallysubstituted C₁₋₆ perhaloalkyl, optionally substituted aryl, optionallysubstituted heteroaryl, and optionally substituted benzyl;

either:

i) Y is selected from the group consisting of C₁₋₆ carboxylate, C₁₋₆amide, OR^(L), halide, amide, thiolate, oxoanion, C₁₋₆ alkyl, optionallysubstituted C₁₋₆ alkyl, optionally substituted C₃-C₈ cycloalkyl,optionally substituted C₂-C₈ alkenyl, optionally substituted C₂-C₈alkynyl, optionally substituted C₁-C₈ heteroalkyl, optionallysubstituted C₃-C₈ heterocycloalkyl, optionally substituted C₂-C₈heteroalkenyl, optionally substituted C₁₋₆ perhaloalkyl, optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted benzyl; and L is selected from the group consisting ofabsent, CO, tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O,benzene, toluene, cyclohexene, cyclooctene, cyclooctadiene,cyclopentene, pyridine, diethyl ether, acetonitrile, triphenylphosphine, N-heterocyclic carbenes, C₁₋₆ alcohols, pyrrole, pyrimidine,pyrrolidine, imidazole, and

orii) Y and L are a single bidentate ligand selected from the groupconsisting of C₁₋₆ carboxylate and C₁₋₆ amide; and

each instance of R^(L) is independently selected from the groupconsisting of H, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₂-C₈ alkenyl,optionally substituted C₂-C₈ alkynyl, optionally substituted C₁-C₈heteroalkyl, optionally substituted C₃-C₈ heterocycloalkyl, optionallysubstituted C₂-C₈ heteroalkenyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl.

In certain embodiments, Y is not acetate. In other embodiments, whereinY and L are a single bidentate ligand, Y and L are not acetate.

In certain embodiments, Z is H.

In certain embodiments, the compound of formula (III) is a compound offormula (IIIa):

wherein R¹, R², R³, R^(L), X, Y, Z and L are as defined in formula(III).

In other embodiments, the compound of formula (III) is:

wherein Y is as defined in formula (III) and L is

In certain embodiments, the compound of formula (III) comprises an Ir(III).

In certain embodiments, the compound of formula (III) can form acompound of formula (IV) through reductive elimination of Z—Y:

wherein R¹, R², R³, R^(L), X, Y, Z and L are defined as in formula(III).

In certain embodiments wherein Z is H, the compound of formula (III) canbe contacted with a strong base to form a compound of formula (IV):

wherein R¹, R², R³, R¹⁻, X, Y and L are defined as in formula (III).

In certain embodiments, the compound of formula (IV) comprises an Ir(I).

Methods

The compounds of formula (I), formula (II) or formula (III) can be usedin coupling reactions to promote the catalytic formation of C—C bondsbetween olefins. In certain embodiments, the compounds of formula (I),formula (II) or formula (III) can be used to promote the reactiondepicted in Scheme 1:

wherein each instance of R^(L) and is independently selected from thegroup consisting of H, optionally substituted C₁₋₆ alkyl, optionallysubstituted C₃-C₈ cycloalkyl, optionally substituted C₂-C₈ alkenyl,optionally substituted C₂-C₈ alkynyl, optionally substituted C₁-C₈heteroalkyl, optionally substituted C₃-C₈ heterocycloalkyl, optionallysubstituted C₂-C₈ heteroalkenyl, optionally substituted C₁₋₆perhaloalkyl, optionally substituted aryl, optionally substitutedheteroaryl, and optionally substituted benzyl.

In certain embodiments, the olefins comprise at least one vinylichydrogen.

In certain embodiments, the invention includes a method of catalyticallycoupling two or more olefins to form a single di-unsaturated molecule.In certain embodiments, the two or more olefins are identical. In otherembodiments, at least one olefin is distinct from at least one otherolefin.

In certain embodiments, the method comprises contacting a compound offormula (I) with an olefin. In other embodiments, the method comprisescontacting a compound of formula (II) with an olefin. In yet otherembodiments, the method comprises first contacting a compound of formula(III), wherein Z is H, with a strong base, whereby the hydride and Yligand are removed from the metal center to form a catalytically activecompound of formula (IV), which is then contacted with an olefin.

In certain embodiments, the compound of formula (I), (II), or (IV) iscontacted with the olefin under high pressure. In other embodiments, theolefin pressure ranges from about 2 atm to about 12 atm, but it notnecessarily limited to this range.

In certain embodiments, the compound of formula (I), (II), or (IV) iscontacted with the olefin at a temperature of about 100° C. to about200° C. In other embodiments, the olefin is contacted at a temperatureof about 100° C. to about 110° C.

In certain embodiments, the compound of formula (I), (II), or (IV) iscontacted with the olefin in solution. In other embodiments, thesolution is a non-aqueous solution. In yet other embodiments, thesolution comprises a solvent selected from, but not necessarily limitedto, the group consisting of toluene, benzene, xylenes, dioxane, heptane,pyridine, tetrahydrofuran, acetone, acetonitrile, butanol, butanone,carbon tetrachloride, chlorobenzene, chloroform, cyclohexane,dichloroethane, diethylene glycol, diethyl ether, diglyme, dimethylformamide, dimethyl sulfoxide, ethanol, ethyl acetate, ethylene glycol,glycerin, hexamethylphosphoramide, hexamethylphosphorous triamide,hexanes, methanol, methylene chloride, N-methyl-2-pyrrolidinone,nitromethane, pentane, petroleum ether, propanol and trimethylamine.

In certain embodiments, the solution further comprises at least oneacceptor capable of accepting an equivalent of H₂. In other embodiments,the acceptor is a hydrogen acceptor. In yet other embodiments, theacceptor is an olefin. In yet other embodiments, the acceptor is anadditional equivalent of olefin A or B from Scheme 1.

In certain embodiments, the olefins are ethylene. In other embodiments,the conjugated 1,3-diene product is 1,3-butadiene.

In certain embodiments, the method comprises contacting a compound offormula

wherein L is

with ethylene.

In certain embodiments, the method further comprises removing thedi-unsaturated product from the reaction mixture as it is produced. Inother embodiments, the di-unsaturated product is removed from thereaction mixture in vacuo. In yet other embodiments, the di-unsaturatedproduct is removed from the reaction mixture through distillation. Incertain embodiments, by removing the di-unsaturated product from thereaction mixture as it is produced, the overall reaction yield andselectivity is increased.

The invention further provides methods, as well as systems which utilizethe compounds and methods of the invention, for converting an organicfeedstock to a conjugated 1,3-diene.

In certain embodiments, the method comprises subjecting an organicfeedstock to a cracking process in order to produce ethylene, and thencontacting the ethylene product with a compound of formula (I), formula(II) or formula (IV) in order to produce 1,3-butadiene. In otherembodiments, the organic feedstock is selected from the group consistingof shale gas, methane and ethane.

In certain embodiments, the cracking process does not completely convertall of the organic starting materials into ethylene. In otherembodiments, the mixed cracking products can be contacted with compoundof formula (I), formula (II) or formula (IV) and then any non-butadieneorganics (unreacted organics as well as any potential organic byproductssuch as ethane, butane and butene) can be recycled and re-subjected tothe cracking process (FIG. 6).

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, numerous equivalents to thespecific procedures, embodiments, claims, and examples described herein.Such equivalents were considered to be within the scope of thisinvention and covered by the claims appended hereto. For example, itshould be understood, that modifications in reaction conditions,including but not limited to reaction times, reaction size/volume, andexperimental reagents, such as solvents, catalysts, pressures,atmospheric conditions, e.g., nitrogen atmosphere, andreducing/oxidizing agents, with art-recognized alternatives and using nomore than routine experimentation, are within the scope of the presentapplication.

It is to be understood that, wherever values and ranges are providedherein, the description in range format is merely for convenience andbrevity and should not be construed as an inflexible limitation on thescope of the invention. Accordingly, all values and ranges encompassedby these values and ranges are meant to be encompassed within the scopeof the present invention. Moreover, all values that fall within theseranges, as well as the upper or lower limits of a range of values, arealso contemplated by the present application. The description of a rangeshould be considered to have specifically disclosed all the possiblesub-ranges as well as individual numerical values within that range and,when appropriate, partial integers of the numerical values withinranges. For example, description of a range such as from 1 to 6 shouldbe considered to have specifically disclosed sub-ranges such as from 1to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6,and so on, as well as individual numbers within that range, for example,1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadthof the range.

The following examples further illustrate aspects of the presentinvention. However, they are in no way a limitation of the teachings ordisclosure of the present invention as set forth herein.

EXAMPLES

The invention is now described with reference to the following Examples.These Examples are provided for the purpose of illustration only, andthe invention is not limited to these Examples, but rather encompassesall variations that are evident as a result of the teachings providedherein.

Materials & Methods

Unless specified otherwise, all reactions were conducted under an argonatmosphere using an MBraun glovebox, or Schlenk or vacuum-linetechniques. Anhydrous benzene and p-xylene were purchased fromSigma-Aldrich, stored over molecular sieves in the glovebox and usedwithout further purification. Benzene-d₆, toluene-d₈ and p-xylene-d₁₀were purchased from Cambridge Isotope Labs, dried over activated aluminaand filtered. All other reagents were purchased from commercialsuppliers and used without further purification. Medium-walled NMR tubes(maximum pressure: 150 psi) and heavy-walled Wilmad quick pressure valveNMR tubes (maximum pressure: 200 psi) were purchased from Sigma-Aldrich.NMR spectra were acquired on 500 MHz Varian VNMRS NMR spectrometers and¹H and ¹³C spectra are referenced to residual solvent peaks. The signalof the residual protio methyl group of p-xylene-d₁₀ was set at δ 20.90in the ¹³C NMR spectrum.

Synthesis and Characterization of Complexes

(Phebox)Ir(OAc)₂(OH₂)

(Phebox)Ir(OAc)₂(OH₂) was prepared according to published procedures(Ito, J.-i.; Shiomi, T.; Nishiyama, H. Adv. Synth. Catal. 2006, 348,1235-1240). Briefly, a mixture of Phebox-H, IrCl₃(H₂O)₃, and NaHCO₃ washeated in methanol to give (Phebox)Ir(Cl)₂(H₂O). This was converted tothe acetate complex (Phebox)Ir(OAc)₂(OH₂) by treatment with an excess ofsilver acetate in high yield.

(Phebox)Ir(OAc)(H) (1)

(Phebox)Ir(OAc)₂(OH₂) (50 mg, 0.0080 mmol) and 5 mL 2-propanol wereadded to a 50-mL Teflon-stoppered reaction vessel under argon atmosphereand then heated at 100° C. for 2 h. Volatiles were then removed invacuo. Complex 2 was obtained in 98% yield (by NMR). Furtherpurification was achieved by recrystallization from diethylether/pentane at −32° C. 1H NMR (C₆D₆, 500 MHz): δ6.49 (s, 1H), 3.85 (d,J=8.3 Hz, 2H), 3.80 (d, J=8.3 Hz, 2H), 2.64 (s, 6H), 2.05 (s, 3H), 1.33(s, 6H), 1.29 (s, 6H), −33.80 (s, 1H). 13C NMR (C₆D₆, 125 MHz): δ185.8,178.6, 177.2, 139.4, 126.9, 123.0, 81.6, 65.7, 27.3, 26.6, 26.3, 18.9.Anal. Calcd. for 2-H: C, 43.54; H, 4.93; N, 5.08. Found: C, 43.11; H:4.74; N, 4.70.

(Phebox)Ir(η²-ethylene)₂ (2)

1 (11 mg, 0.020 mmol) and 2.5 mL benzene were added to a 25-mL Schlenkflask in a glovebox. The flask was removed from the glovebox and chargedwith 1 atm of ethylene. A benzene solution of NaOtBu (4.8 mg, 0.050mmol) was added via syringe dropwise through the septum at roomtemperature. After 24 h, the volatiles were removed under vacuum and theproduct was redissolved in toluene (2.5 mL). The clear solution wasfiltered using a cannula filter. Subsequently, the residue was washedwith additional toluene (2.5 mL) and then combined with initial toluenesolution. Removal of the volatiles under vacuum resulted in a brightorange powder. Yield: 8.3 mg (76%). 1H NMR (C₆D₆, 500 MHz): δ6.68 (s,1H), 3.41 (s, 4H), 3.45-3.32 (m, 4H), 2.66 (s, 6H), 1.65-1.50 (m, 4H),0.73 (s, 12H). 13C NMR (C₆D₆, 125 MHz): δ211.1, 178.0, 138.2, 129.0,126.6, 81.3, 67.8, 31.9, 26.4, 19.0, 10.8. Anal. Calcd. for 3: C, 48.24;H, 5.71; N, 5.11. Found: C, 47.78; H: 5.40; N, 4.86.

(Phebox)Ir(C₄H₈)(C₂H₄) (3)

2 (2.2 mg, 4.0 μmol) and 0.4 mL p-xylene (2.0 mM) in C₆D₆ solution wereadded to a J-Young NMR tube in the glovebox. The solution was degassedusing one freeze-pump-thaw cycle, charged with 1 atm of ethylene andheated at 70° C. for 18 h. NMR yield: 71%. ¹H NMR (C₆D₆, 500 MHz): δ6.66 (s, 1H), 3.74 (t, J=7.1 Hz, 2H), 3.55 (d, J=8.2 Hz, 2H), 3.48 (d,J=8.2 Hz, 2H), 2.86 (br s, 4H), 2.64 (s, 6H), 2.55 (m, 2H), 2.17 (m,2H), 1.53 (t, J=6.8 Hz, 2H), 1.13 (s, 6H), 0.82 (s, 6H). ¹³C NMR (C₆D₆,125 MHz): δ 204.8, 178.0, 139.7, 127.0, 126.7, 81.6, 67.7, 53.2, 40.6,36.4, 29.9, 27.9, 27.4, 19.1, 2.7.

(Phebox)Ir(η²-ethylene-¹³C₂)₂ (2-¹³C₄)

(Phebox)Ir(OAc)(H) (4.4 mg, 8.0 μmol), NaO^(t)Bu (2.2 mg, 24 μmol) and0.5 mL p-xylene were added to a J-Young NMR tube in the glovebox. Thesolution was degassed using one freeze-pump-thaw cycle and charged with1 atm of ethylene-¹³C₂. After heating at 40° C. for 4 h, the volatileswere removed under vacuum and the product was re-dissolved in toluene (1mL). Bright orange powder was achieved after filtration and removal ofsolvent under vacuum. Yield: 3.2 mg (73%). ¹H NMR (p-xylene-d₁₀, 500MHz): 6.61 (s, 1H), 3.57 (s, 4H), 3.45-3.03 (m, ¹J¹³ _(C—H)=151.6 Hz,4H), 2.65 (s, 4H), 1.60-1.18 (m, 4H), 0.82 (s, 12H). ¹³C NMR ofethylene-¹³C₂ ligand (p-xylene-d₁₀, 125 MHz): δ 32.8 (d, J=41.7 Hz),11.6 (d, J=41.9 Hz).

(Phebox)Ir(C₄H₈-¹³C₄)(C₂H₄-¹³C₂)(3-¹³C₆)

Following the procedure above to synthesize 3, 2-¹³C₄ (10 mM) inp-xylene-d₁₀ solution (0.4 mL) was heated under ethylene-¹³C₂ (1 atm) at70° C. for 18 h. NMR yield: 70%. ¹³C NMR of ¹³C labelled ligand(p-xylene-d₁₀, 125 MHz): δ 54.1, 41.3 (ddd, J=36.7, 32.3, 4.2 Hz), 37.2(dd, J=36.9, 31.9 Hz), 31.2-29.8 (m), 3.5 (dd, J=32.0, 4.3 Hz).

(Phebox)Ir(C₄H₈-¹³C₄)(C₂H₄) (3-¹³C₄)

3-¹³C₆ (7.0 mM) and 2-¹³C₄ (3.0 mM) in p-xylene-d₁₀ solution (0.4 mL)was added to a J-Young NMR tube in the glovebox. The solution wasdegassed using one freeze-pump-thaw cycle and charged with 1 atm ofethylene. 3-¹³C₄ (7.0 mM) and 2 (3.0 mM) was formed at room temperature.¹³C NMR of ¹³C labelled ligand (p-xylene-d₁₀, 125 MHz): δ 41.3 (ddd,J=36.6, 32.3, 4.2 Hz), 37.2 (dd, J=36.8, 32.1 Hz), 31.6-29.6 (m), 3.5(dd, J=32.0, 4.3 Hz).

1,3-Butadiene-³C₄

3-¹³C₆ (7.0 mM) and 2-¹³C₄ (3.0 mM) in p-xylene-d₁₀ solution (0.4 mL)was added to a medium-walled and sealable NMR tube, which was connectedto a Kontes high-vacuum adapter with Tygon tubing. The Kontes valve wasattached to a vacuum-gas manifold and the solution was frozen withliquid nitrogen. The headspace of NMR tube was evacuated until thepressure reached 10 mTorr. The headspace was filled with 1 atm ofethylene-¹³C₂ and then condensed using liquid nitrogen. After 30seconds, the NMR tube was sealed using an oxygen torch (the headspacevolume was decreased by 50%, which brought the total ethylene pressureto 2 atm). The sealed NMR tube was allowed to reach room temperature,then heated and rotated in a GC oven at 100° C. for 1 h. ¹³C NMR(p-xylene-d₁₀, 125 MHz): δ 143.3-142.1 (m), 122.7-121.1 (m).

(Phebox)Ir(OAc)(CH₂(CH₂)₂CH₃) (4)

Following a procedure outlined in Gao, Y, et al. J. Am. Chem. Soc. 2017,139, 6338, the reaction was set up under 1 atm of 1-butene and finishedin 15 minutes at room temperature. Briefly, 1 (2.2 mg, 0.004 mmol),NaBArF (0.6 mg, 0.7 μmol), 400 μL of benzene and 10 μL of 0.117 Mdioxane in benzene solution were added to a J-Young NMR tube in aglovebox. The solution was degassed using one freeze-pump-thaw cycle andthen charged with 1 atm of 1-butene. The reaction was finished in 15minutes at room temperature.

NMR yield: 98%. ¹H NMR (C₆D₆, 500 MHz): δ 6.48 (s, 1H), 3.86-3.80 (m,4H), 2.64 (s, 6H), 2.07 (s, 3H), 1.69 (m, 2H), 1.41 (m, 2H), 1.36 (s,6H), 1.28 (s, 6H), 0.98 (m, 3H), 0.63-0.51 (m, 2H). ¹³C NMR (C₆D₆, 125MHz): δ 184.3, 182.1, 177.3, 139.3, 126.0, 123.2, 82.0, 66.2, 33.7,27.2, 27.0, 25.9, 24.6, 19.0, 14.6, −3.8.

(Phebox)Ir(C₄H₈)(CO) (6)

3 (7.0 mM) and 2 (3.0 mM) in C₆D₆ solution (0.4 mL) was added to aJ-Young NMR tube in the glovebox. The solution was degassed using onefreeze-pump-thaw cycle and charged with 1 atm of CO. 6 (7.0 mM) and 5(3.0 mM) was formed at room temperature. ¹H NMR of 6 (C₆D₆, 500 MHz): δ6.61 (s, 1H), 3.70-3.58 (m, 4H), 3.24 (t, J=7.1 Hz, 2H), 2.58 (s, 7H),2.47 (m, 2H), 2.14 (m, 2H), 1.18 (s, 6H), 1.13 (s, 6H), 1.02 (t, J=6.8Hz, 2H). ¹³C NMR of 6 (C₆D₆, 125 MHz): δ 194.7, 178.6, 175.6, 140.4,127.4, 127.0, 81.4, 67.1, 39.3, 36.9, 32.7, 28.4, 28.3, 19.1, 1.2.

(Phebox)Ir(CO) (5)

6 (7.0 mM) and 5 (3.0 mM) in C₆D₆ solution (0.4 mL) was added to aJ-Young NMR tube in the glovebox. After heating at 90° C. for 1 h, thevolatiles were removed under vacuum and the products were re-dissolvedin C₆D₆. 5 (8.2 mM) was obtained with free Phebox-H (1.5 mM) as the sideproduct. ¹H NMR (C₆D₆, 500 MHz): δ 6.40 (s, 1H), 3.73 (s, 4H), 2.30 (s,6H), 1.17 (s, 12H). ¹³C NMR (C₆D₆, 125 MHz): δ 199.8, 199.3, 177.7,135.5, 131.6, 129.3, 80.5, 65.8, 28.1, 19.0.

Dehydrogenative Coupling Conditions With Ethylene (2 Atm or 8 Atm)

400 μL of 2 (5.0 mM) and p-xylene (3.0 mM) in toluene-d₈ solution wasadded to a medium-walled and sealable NMR tube, which was connected to aKontes high-vacuum adapter with Tygon tubing. The Kontes valve wasattached to a vacuum-gas manifold and the solution was frozen withliquid nitrogen. The headspace of the NMR tube was evacuated until thepressure reached 10 mTorr. The headspace was filled with 1 or 4 atmethylene which was condensed by immersion in liquid nitrogen. After 30sec, the NMR tube was sealed using an oxygen torch (the headspace volumewas decreased by 50%, which brought the total ethylene pressure to 2 atmor 8 atm). The sealed NMR tube was allowed to reach room temperature,then heated while being rotated in a gas chromatography (GC) oven topromote gas-liquid mixing.

With Ethylene (12 Atm)

200 μL of 2 (5.0 mM) and p-xylene (3.0 mM) in toluene-d₈ solution wastransferred to a heavy-walled NMR tube fitted with a re-sealable Teflonvalve in a glovebox. The solution was degassed with a freeze-pump-thawcycle and charged with 12 atm ethylene. The NMR tube was heated in anoil bath and shaken every 1 hour to promote gas-liquid mixing.

In the Presence of 1-Butene

200 μL of 2 (5.0 mM) and p-xylene (3.0 mM) in toluene-d₈ solution wastransferred to a heavy-walled NMR tube fitted with a re-sealable Teflonvalve in a glovebox. The solution was degassed with a freeze-pump-thawcycle and charged with 2 psi of 1-butene. After shaking to promotegas-liquid mixing, the NMR tube was charged with 8 atm ethylene. Theconcentration of 1-butene in solution was determined to be 7.7 mM by ¹HNMR spectroscopy. The NMR tube was heated in an oil bath and shakenevery 1 hour to promote gas-liquid mixing.

In the Presence of 1,3-Butadiene

200 μL of 2 (5.0 mM) and p-xylene (3.0 mM) in toluene-d₈ solution and 20μL of 1,3-butadiene (ca. 15 wt. %) in hexane solution was added to aheavy-walled NMR tube fitted with a re-sealable Teflon valve in aglovebox. The solution was degassed with a freeze-pump-thaw cycle andcharged with 8 atm ethylene. The NMR tube was heated in an oil bath andshaken every 1 hour to promote gas-liquid mixing.

Ratio of 3 to 2 During Reaction

Following the procedure titled “With ethylene (2 atm or 8 atm)”,reaction solutions with 2 atm, 4 atm, 6 atm and 8 atm ethylene wereprepared, heated at 100° C. and monitored by ¹H NMR spectroscopy every25 min. The ratio of 3 to 2 was found to reach a steady state after 150min. (Table 1)

TABLE 1 Ratio of 3 to 2 in the reaction under different pressure ofethylene. PC₂H₄ 2 atm 4 atm 6 atm 8 atm [3]/[2] 1.5 1.6 1.5 1.6

Gas Chromatographic Analysis Method

GC analyses (FID detection) were performed on a Varian 430-GC instrumentfitted with Agilent J&W GS-GasPro column (60 m length, 0.32 mm ID) usingthe following method: Starting temperature: 40° C.; Time at startingtemp: 1.4 min; Ramp1: 8° C./min up to 150° C. with hold time 3 min;Ramp2: 20° C./min up to 260° C. with hold time 30 min; Flow rate(carrier): 1.4 mL/min (N₂); Split ratio: 25; Injector temperature: 250°C.; Detector temperature: 260° C.

Computational Methods

All electronic structure calculations employed the DFT method. The M06-Lexchange-correlation functional was used with the following choices ofatomic basis sets: for Ir, the SDD relativistic effective (small) corepotential and associated (6s5p3d) valence basis set, augmented with anf-type function and a complete set of diffuse spdf-type functions wereapplied (Andrae, et al. Theor. Chim. Acta., 1990, 77, 123-141; Iron, etal. J. Am. Chem. Soc., 2004, 126, 11699-11710); all-electron 6-311G(d,p)basis sets were applied to all other atoms(M06-L/SDD(+f+spdf)/6-311G(d,p)) (Ditchfield et al., J. Chem. Phys.,1971, 54, 724-728; Hariharan, et al., Molecular Physics, 1974, 27,209-214; Raghavachari, et al., J. Chem. Phys., 1980, 72, 650-654).Reactant, transition state and product geometries were fully optimizedusing standard optimization procedures and characterized by normal modeanalysis. For transition states (TSs) possessing an ‘imaginary’frequency above ca. 100i cm⁻¹, the TS was connected to itsrepresentative reactant/product by carrying out Intrinsic ReactionCoordinate (IRC) calculations (Hratchian, et al., J. Chem. Theory andComput. 2005, 1, 61-69). In some cases (small ‘imaginary’ frequencies),manually displacement of the TS structures in opposite directions alongthe transition vector (using GaussView8) was used, followed by geometryoptimization toward a minimum to properly locate the matchingreactant/product. Expanded integration grid sizes (pruned (99,590)atomic grids invoked in Gaussian 09 using the integral=ultrafinekeyword) were applied to increase numerical accuracy and stability ingeometry optimizations as well as normal mode analysis (Frisch, et al.,Trucks Gaussian 09 User's Reference, 147). The (unscaled) vibrationalfrequencies formed the basis for the calculation of vibrationalzero-point energy (ZPE) corrections. Standard thermodynamic corrections(based on the harmonic oscillator/rigid rotor approximations and idealgas behavior) were made to convert from purely electronic potentialenergies (E) to (standard) enthalpies (H°, T=298.15 K) and Gibbs freeenergies (G°; T=298.15 K, P=1.0 atm). The polarizable conductorself-consistent reaction field model (CPCM; Barone, et al., J. Phys.Chem. A, 1998, 102, 1995-2001) was applied in all calculations to probegeneral bulk solvation effects. The solvent used experimentally in thisstudy, p-xylene, was modeled using default parameters built into thechosen electronic structure code (Gaussian 09). All calculations wereexecuted using the Gaussian 09 series of computer programs (RevisionD.01).

Example 1: Catalytic Dehydrogenative Coupling of Ethylene Catalyzed by 2

Upon heating a toluene-d₈ solution of 2 (5.0 mM) under ethylene (2 atm)at 100° C. for 4 h, 1,3-butadiene (8.0 mM) and ethane (3.0 mM) wereobserved in solution by ¹H NMR spectroscopy (eq 1). Surprisingly, only aminimal concentration of butenes (<1.0 mM) was observed in the ¹H NMRspectrum, comprising only 8% of C₄ products (entry 1, Table 2) asdetermined by gas chromatography (GC).

When an identical solution was heated for a longer time (16 h) the yieldof butadiene was higher but the amount of butene as a percentage of C₄products was significantly greater 21% (entry 2, Table 2). The latterobservation suggests that the butadiene observed at the shorter reactiontime was not a secondary product formed by the dehydrogenation ofbutene; it is instead consistent with the converse possibility that thebutenes observed are formed as secondary products from butadienehydrogenation.

Under higher pressures of ethylene (8 atm and 12 atm; entries 3 and 4,Table 2) greater yields of butadiene were obtained, with a relativelylower yield of butenes. When butadiene was added initially to thesolution (entry 5), the net production of butadiene was much less, whilethe production of butene was significantly greater, consistent with theproposal that the butene is formed from butadiene. Accordingly, when thereaction is taken to higher conversion (with slightly longer times and aslightly higher temperature of 110° C.) significant yields of butene areobtained (entries 6-8). The formation of C₆ olefins is also observed atlater times suggesting that these are also secondary products.

By removing the volatiles periodically (every 5.5 h) and replacingsolvent and ethylene, greater total yields of butadiene and selectivitywere achieved. After 21 h (4 cycles) a total of 101 mM butadiene hadbeen produced, comprising 76% of the total olefins (entry 9, Table 2;FIG. 1).

TABLE 2 Dehydrogenative Ethylene Coupling Catalyzed by 2 temp/butadiene/mM butenes/ C₆/ entry ° C. time ^(P)C₂H₄ (% total olefins) mMmM 1 100  4 h 2 atm 8.0 (92%) <1.0 0 2 100 16 h 2 atm 15 (68%) 4.1 2.2 3100 12 h 8 atm 23 (88%) 2.1 1.3 4 100 12 h 12 atm 20 (90%) 2.2 0 5 100^(b)  6 h 8 atm 6.1 (47%) 6.2 0.7 6 110 18 h 8 atm 65 (62%) 28 12 7110 18 h 12 atm 70 (71%) 20 8.2 8 110 21 h 12 atm 67 (62%) 30 12 9 110^(c) 21 h 12 atm 101 (76%) 21 11 ^(a)2 (5 mM) in toluene-d₈. Topromote gas-liquid mixing the NMR tube was shaken periodically (entries1-5, sealed NMR tube in an oven equipped with an internal rotator;entries 6-9, high-pressure J-Young tube manually shaken every 1 h).^(b)73 mM added butadiene. ^(c)Volatiles removed every 5.5 h followed byrecharging with toluene-d₈ and ethylene.

Example 2: Identification of Catalytic Intermediate Species

A toluene-d₈ solution of 2 was prepared with added 1-butene (7.7 mM).After 2 h at 100° C., under 8 atm ethylene, 8.8 mM butadiene had formedwhich was no different from an identical solution to which 1-butene hadnot been added. There was no change in the concentration of 1-butene,indicating that the butadiene was not formed from 1-butene. In addition,a similar experiment was conducted with added 1-butene (30 mM,isotopically unlabeled) under 2 atm ethylene-d₄. The resulting butadienewas completely butadiene-d₆, while the concentration of unlabeled1-butene was unchanged, proving that the butadiene formation does notproceed via free 1-butene.

In the course of the catalytic runs (5 mM 2, ethylene, toluene-d₈, 100°C.), ¹H NMR spectroscopy revealed the presence of a new species 3, alongwith 2. The ratio of 3 to 2 reached a steady state within ca. 4 h. Itwas found to be independent of ethylene pressure over a range from 2atm-8 atm, with [3]/[2]=1.6±0.1.

The ¹H NMR spectral data for 2 indicates C_(s) symmetry, in contrastwith the C_(2v) symmetry of 2. A set of four multiplets is observed atδ1.53 (2H), δ 2.18 (2H), δ 2.55 (2H) and δ 3.74 ppm (2H). HCOSY NMRspectral data is consistent with the assignment of these peaks to a1,4-butanediyl ligand. A broad singlet indicative of an ethylene ligand,is observed at δ 2.86 ppm (4H) with a corresponding signal at δ 53.19ppm in the ¹³C NMR spectrum. Signals in the ¹³C NMR spectrum at δ 40.6,δ 36.4, δ 29.9 and δ 2.7 ppm are attributable to the butanediyl group.Based on this data, complex 3 is proposed to be an iridacyclopentaneethylene complex. Isolation of 3 from the mixture with 2 proveddifficult, and attempts to grow X-ray-quality crystals directly from themixture were unsuccessful.

Addition of acetic acid (20 mM) to the C₆D₆ solution of 2 and 3 (3:7),immediately afforded a 3:7 mixture of (phebox)Ir(OAc)(ethyl) (1-ethyl)and (phebox)Ir(OAc)(n-butyl) (4) (eq 2). When an identical solution of 2and 3 was exposed to 1 atm CO, the signals attributable to the ethyleneligands of both compounds quickly disappeared from the ¹H NMR spectrum.The products were identified, on the basis of their ¹H and ¹³C NMRspectra, as (Phebox)Ir(CO) (5) and 6, the product of substitution of theethylene ligand of 2 by CO. X-ray-quality crystals of complex 6 fromthis mixture were obtained, which confirmed assignment of complex 6(FIG. 2A), and by inference, assignment of 3.

When a mixture of 2 (3.0 mM) and 3 (7.0 mM) in p-xylene-d₁₀ solution washeated under argon (1 atm) at 90° C., 2 was observed as the majorspecies after 1 h. Further heating led to the decomposition of 2 withrelease of ethylene and the formation of only trace amounts (<0.5 mM) ofC₄ hydrocarbons (eq 3).

Example 3: X-Ray Structural Data for Complex 6

Single-crystal X-ray diffraction data were collected on a Bruker SmartAPEX CCD diffractometer with graphite monochromatized Mo Kα radiation(λ=0.71073 Å) at 100 K. The crystals were immersed in oil and placed ona glass needle in the cold stream. The data were corrected for Lorenzeffects, polarization, and absorption, the latter by a multi-scan methodusing program SAINT (Bruker (2013). APEX2, SAINT and SADABS. Bruker AXSInc., Madison, Wis., USA). The structures were solved by direct methodsusing program SHELXS (Sheldrick, G. M. (2008). Acta Cryst. A64,112-122.). Using program SHELXL (Sheldrick, G. M. (2015). Acta Cryst.C71, 3-8.) all non-hydrogen atoms were refined based upon Fobs and allhydrogen atom coordinates were calculated with idealized geometries.FIG. 2B depicts the ORTEP diagram of complex 6.

Example 4: Mechanistic Studies

A mixture of 2 and 3 was synthesized with ¹³C₂H₄, which resulted in full¹³C-labeling of the 1,4-butanediyl unit of 3 and the ethylene ligands ofboth 2 and 3. The mixture of 2-¹³C₄ (3.0 mM) and 3-¹³C₆ (7.0 mM) inp-xylene-d₁₀ was then exposed to unlabeled ethylene (2 atm) at roomtemperature. The ethylene-¹³C₂ ligands of both complexes were rapidlysubstituted by unlabeled ethylene ligand while free ethylene-¹³C₂ wasdetected by ¹H NMR and ¹³C NMR spectroscopy. No loss of ¹³C labeling ofthe 1,4-butanediyl group was observed, consistent with the highertemperatures required for interconversion of 2 and 3. Upon heating thismixture of unlabeled 1 and ¹³C₄-butanediyl labeled 3 at 100° C. for 30min under an atmosphere of unlabeled C₂H₄, fully labeled (¹³C₄)butadiene (1.7 mM) was observed in the ¹H NMR spectrum, along with someunlabeled butadiene (0.6 mM). The formation of the ¹³C₄-labeledbutadiene under an atmosphere of unlabeled C₂H₄, particularly as themajor product, rules out the possibility that this butadiene formed viaconversion of 3 to 2, as the latter undergoes rapid exchange with freeethylene.

To determine the mechanism of eq 1, computational investigations (DFT)were undertaken, employing the M06-L functional, the SDD effective corepotential on Ir, and valence basis sets of triple-zeta plus polarizationquality (M06-L/SDD(+f+spdf)/6-311G(d,p)); some effects of solvation byp-xylene were included via a continuum dielectric model (CPCM/p-xylene).Complex 2 was calculated to undergo conversion to iridacyclopentane 3via a concerted mechanism with activation parameters ΔH^(‡)=26.7kcal/mol and ΔS^(‡)=−1.7 eu (ΔG^(‡)=27.2 kcal/mol at T=298 K, P=1 atm)to afford the 16-electron iridacyclopentane 7, followed by rapidcoordination of ethylene to give 3 (FIG. 3). At 100° C. these activationparameters correspond to a rate of 7.6×10⁻⁴ s⁻¹ or a half-life of ca.900 s, in good agreement with the observation, noted above, that thereaction of 2 at 100° C. took several hours to reach a steady stateratio of 2 to 3.

In the case of iridacyclopentane 3, DFT calculations revealed anunanticipated pathway for β-H-elimination. Loss of ethylene from 3returns the 16-electron intermediate 7, which shows signs of stericcrowding including a short H—H distance of 1.97 Å between the H atoms atC2 of the iridacyclopentane ring and the oxazoline methyl group. This isfollowed by the formation of an agostic interaction with a C(2)-H bond(d_(Ir—H)=2.11 Å), requiring the formation of a strongly puckerediridacyclopentane ring. Formation of this agostic complex (8, FIGS. 3and 4B) would be sterically prohibitive but for an accompanying rotationaround an oxazoline-aryl bond and thus loss of an N—Ir bond, i.e. κ³-κ²partial dechelation of the Phebox ligand. The free energy of 8 is 17.2kcal/mol above 2, or 9.4 kcal/mol above the non-agosticiridacyclopentane 7 (note that this energy includes the loss of an Ir—Nbond).

ΔG^(‡) for β-H elimination from agostic complex 8 is 7.2 kcal/mol,corresponding to an overall barrier of 26.3 kcal/mol from 3. The β-Helimination leads to a 3-buten-1-yl hydride complex, 9, with the Pheboxligand still bound in a κ² configuration. Intermediate 9 may bedescribed as approximately square pyramidal with C1 of the 3-buten-1-ylgroup in the apical position (FIG. 4D). The 3-buten-1-yl C═C double bondis approximately trans to the bound N (the N—Ir-centroid angle is 170°)while the hydride is approximately trans to the Ir-bound phebox arylcarbon atom (C—Ir—H=160°). Migration of the hydride to the vacantcoordination site, accompanied by migration of the C═C double bond tothe position formerly occupied by the hydride and coordination of thedangling oxazolinyl N atom would give the 18-electron κ³-Phebox complex10 with a free energy 1.6 kcal/mol above 7.

Without intending to be limited to any particular theory, the apparentease by which the Phebox ligand acts as a hemi-labile ligand, asindicated by the calculations, may be key to the surprisingly lowbarrier to β-H elimination of the metallacyclopentane. It is perhapsalso important that the geometry of Phebox requires that upondechelation the resulting “open” coordination site is not in fact very“open”. The pendant oxazolinyl group necessarily remains close to themetal center, likely too close to allow coordination of another ligand(even one as small as ethylene), but not so close as to preventpuckering of the iridacyclopentane ring or slippage of the resultingbutenyl vinyl group into the vacant coordination site.

β-H-elimination to give 9 may be followed by decoordination of the C—Cdouble bond and re-coordination of the oxazoline N atom to giveκ³-Phebox complex 11 (possibly, but not necessarily, via κ³-Pheboxcomplex 10; FIG. 5). Complex 11 could then undergo C—H elimination togive 1-butene. The calculations predict, however, that the C—Helimination transition state TS3 is 4.6 kcal/mol higher in free energythan TS4 for β-H elimination (pathway shown in blue, FIG. 5). An evenmore favorable pathway, however, is calculated to proceed via insertionof ethylene into the Ir—H bond of 11 (following ethylene coordination togive 12). The free energies of TS4 and TS5 are probably notsignificantly different within the accuracy limits of the calculation,and the relative probability of 11 undergoing ethylene coordination andinsertion (“TS5 pathway”), as opposed to β-H-elimination (“TS4pathway”), may depend on ethylene concentration. Either through the TS4or TS5 pathways, butadiene is formed via β-H-elimination of the3-buten-1-yl group. By the TS4 pathway, (Phebox)IrH₂ (14) is produced,which is expected to undergo facile insertion of ethylene into an Ir—Hbond. The two pathways thereby converge at (Phebox)IrH(Et) (15);elimination of ethane from 15 and coordination of two ethylene moleculesthen completes the catalytic cycle.

By proceeding via dihydride 14, the mechanism allows the possibilitythat 14 will hydrogenate the butadiene product to give 1-butene. This isconsistent with the observation discussed above that higher pressures ofethylene lead to higher ratios of butadiene to 1-butene.

The disclosures of each and every patent, patent application, andpublication cited herein are hereby incorporated herein by reference intheir entirety. While this invention has been disclosed with referenceto specific embodiments, it is apparent that other embodiments andvariations of this invention may be devised by others skilled in the artwithout departing from the true spirit and scope of the invention. Theappended claims are intended to be construed to include all suchembodiments and equivalent variations.

What is claimed is:
 1. A compound of formula (I), or a salt or solvatethereof:

wherein: A is selected from the group consisting of H, OH, halide,amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl,benzyl,

 wherein at least one atom or bond in A is optionally coordinated to theIr; R¹ is selected from the group consisting of H, OH, halide, amine,C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl,C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; eachinstance of R² is independently selected from the group consisting of H,OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl,C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl,heteroaryl, and benzyl; each instance of R³ is independently selectedfrom the group consisting of H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; each instanceof R⁴ is independently selected from the group consisting of H, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, aryl, heteroaryl, and benzyl; X is selected from the groupconsisting of CH₂, NH, O, and S; each occurrence of L is independentlyselected from the group consisting of absent, CO, tetrahydrofuran,furan, pyran, tetrahydropyran, H₂O, benzene, toluene, cyclohexene,cyclooctene, cyclooctadiene, cyclopentene, pyridine, diethyl ether,acetonitrile, triphenyl phosphine, N-heterocyclic carbene, C₁₋₆ alcohol,pyrrole, pyrimidine, pyrrolidine, imidazole, and

 and each instance of R^(L) is independently selected from the groupconsisting of H, C₁₋₆ alkyl, C₃-C₅ cycloalkyl, C₂-C₅ alkenyl, C₂-C₅alkynyl, C₁-C₈ heteroalkyl, C₃-C₅ heterocycloalkyl, C₂-C₈ heteroalkenyl,C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl.
 2. The compound ofclaim 1, wherein the compound of formula (I) is a compound of formula(Ia):


3. The compound of claim 1, wherein the compound of formula (I) is acompound of formula:

wherein L is


4. The compound of claim 1, wherein one instance of L is absent and theother instance of L is selected from the group consisting of absent, CO,tetrahydrofuran, furan, pyran, tetrahydropyran, H₂O, benzene, toluene,cyclohexene, cyclooctene, cyclooctadiene, cyclopentene, pyridine,diethyl ether, acetonitrile, triphenyl phosphine, N-heterocycliccarbene, C₁₋₆ alcohol, pyrrole, pyrimidine, pyrrolidine, imidazole, and


5. A compound of formula (II), or a salt or solvate thereof:

wherein: A is selected from the group consisting of H, OH, halide,amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl,benzyl,

 wherein at least one atom or bond in A is optionally coordinated to theIr; R¹ is selected from the group consisting of H, OH, halide, amine,C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl,C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; eachinstance of R² is independently selected from the group consisting of H,OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl,C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl,heteroaryl, and benzyl; each instance of R³ is independently selectedfrom the group consisting of H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; each instanceof R⁴ is independently selected from the group consisting of H, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, aryl, heteroaryl, and benzyl; X is selected from the groupconsisting of CH₂, NH, O, and S; each occurrence of L is independentlyselected from the group consisting of absent, CO, tetrahydrofuran,furan, pyran, tetrahydropyran, H₂O, benzene, toluene, cyclohexene,cyclooctene, cyclooctadiene, cyclopentene, pyridine, diethyl ether,acetonitrile, triphenyl phosphine, N-heterocyclic carbene, C₁₋₆ alcohol,pyrrole, pyrimidine, pyrrolidine, imidazole, and

 and each instance of R^(L) is independently selected from the groupconsisting of H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈alkynyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl,C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl.
 6. The compound ofclaim 5, wherein the compound of formula (II) is:

wherein L is


7. A method of catalytically converting an olefin comprising at leastone vinylic hydrogen to a conjugated 1,3-diene, the method comprisingcontacting the olefin with a compound of formula (I), or a salt orsolvate thereof:

wherein: A is selected from the group consisting of H, OH, halide,amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl,benzyl,

 wherein at least one atom or bond in A is optionally coordinated to theIr; R¹ is selected from the group consisting of H, OH, halide, amine,C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl,C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; eachinstance of R² is independently selected from the group consisting of H,OH, halide, amine, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl,C₃-C₈ heterocycloalkyl, C₁₋₆ perhaloalkyl, C₁₋₆ alkoxy, aryl,heteroaryl, and benzyl; each instance of R³ is independently selectedfrom the group consisting of H, OH, halide, amine, C₁₋₆ alkyl, C₃-C₈cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, C₁₋₆ alkoxy, aryl, heteroaryl, and benzyl; each instanceof R⁴ is independently selected from the group consisting of H, C₁₋₆alkyl, C₃-C₈ cycloalkyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₁₋₆perhaloalkyl, aryl, heteroaryl, and benzyl; X is selected from the groupconsisting of CH₂, NH, O, and S; each occurrence of L is independentlyselected from the group consisting of absent, CO, tetrahydrofuran,furan, pyran, tetrahydropyran, H₂O, benzene, toluene, cyclohexene,cyclooctene, cyclooctadiene, cyclopentene, pyridine, diethyl ether,acetonitrile, triphenyl phosphine, N-heterocyclic carbene, C₁₋₆ alcohol,pyrrole, pyrimidine, pyrrolidine, imidazole, and

 and each instance of R^(L) is independently selected from the groupconsisting of H, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈alkynyl, C₁-C₈ heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl,C₁₋₆ perhaloalkyl, aryl, heteroaryl, and benzyl.
 8. The method of claim7, wherein the compound of formula (I) is a compound of formula (IV) andwherein the method comprises first contacting a compound of formula(III) with a strong base (B) to generate a compound of formula (IV), andthen contacting the compound of formula (IV) with the olefin, wherein:

wherein either: i) Y is selected from the group consisting of C₁₋₆carboxylate, C₁₋₆ amide, OR^(L), halide, amide, thiolate, oxoanion, C₁₋₆alkyl, C₁₋₆ alkyl, C₃-C₈ cycloalkyl, C₂-C₈ alkenyl, C₂-C₈ alkynyl, C₁-C₈heteroalkyl, C₃-C₈ heterocycloalkyl, C₂-C₈ heteroalkenyl, C₁₋₆perhaloalkyl, aryl, heteroaryl, and benzyl; and L′ is selected from thegroup consisting of absent, CO, tetrahydrofuran, furan, pyran,tetrahydropyran, H₂O, benzene, toluene, cyclohexene, cyclooctene,cyclooctadiene, cyclopentene, pyridine, diethyl ether, acetonitrile,triphenyl phosphine, N-heterocyclic carbenes, C₁₋₆ alcohols, pyrrole,pyrimidine, pyrrolidine, imidazole, and

or ii) Y and L′ are a single bidentate ligand selected from the groupconsisting of C₁₋₆ carboxylate and C₁₋₆ amide.
 9. The method of claim 7,wherein the olefin pressure ranges from about 0.1 atm to about 100 atm.10. The method of claim 7, wherein the catalyst is contacted with thealkene at a temperature of about 100° C. to about 200° C.
 11. The methodof claim 7, wherein the olefin comprises ethylene.
 12. The method ofclaim 7, wherein the conjugated 1,3-diene comprises 1,3-butadiene. 13.The method of claim 7, wherein the catalyst is in solution.
 14. Themethod of claim 13, wherein the solution comprises at least one solventselected from the group consisting of toluene, benzene, xylenes,dioxane, heptane, pyridine, tetrahydrofuran, acetone, acetonitrile,butanol, butanone, carbon tetrachloride, chlorobenzene, chloroform,cyclohexane, dichloroethane, diethylene glycol, diethyl ether, diglyme,dimethyl formamide, dimethyl sulfoxide, ethanol, ethyl acetate, ethyleneglycol, glycerin, hexamethylphosphoramide, hexamethylphosphoroustriamide, hexanes, methanol, methylene chloride,N-methyl-2-pyrrolidinone, nitromethane, pentane, petroleum ether,propanol and triethylamine.
 15. The method of claim 13, wherein thesolution further comprises at least one hydrogen acceptor additive.